Karin E Zimmer's PhD research shows that persistent organic pollutants (POPs), such as PCB and mixtures of different POPs, affect the way the adrenal cortex functions and thereby the synthesis of the stress hormone cortisol.

Cortisol plays an important role in normal foetal development and, later in life, in retaining normal body functions during periods of stress. Less research has been carried out on the effects of POPs on cortisol levels than on sex hormones.

POPs are widespread in nature and all animals and humans are exposed to them daily, mainly through food. There have been great concerns regarding the potential ability of these pollutants to affect the body's hormone balance. Zimmer's thesis sheds light on how exposure during early life stages interferes with hormone levels and may therefore cause harm to health later in life. Zimmer also investigated how the production of hormones such as cortisol and sex hormones were affected by environmental mixtures of POPs extracted from fish.

The thesis reveals that exposure to PCBs during foetal life and the suckling period caused altered cortisol levels in the blood of both foetuses and adult animals. This indicates that exposure during these sensitive, initial stages of life may have long-term consequences. Her findings are important because altered cortisol balance during early life may lead to a predisposition to develop several diseases in adulthood, such as diabetes and cardiovascular diseases.

Knowledge about how POPs work and how different POPs act together is important for the assessment of human health risks. Zimmer used human hormone-producing cells in her study. High levels of brominated flame retardants in a POP mixture extracted from fish in Lake Mjøsa in Norway did not make this mixture more potent as regards increasing hormone synthesis than a similar fish mixture from another lake with considerably lower levels. Another POP mixture extracted from crude, unprocessed cod liver also had a pronounced affect on the synthesis of cortisol and sex hormones, whereas a mixture from processed, commercial cod liver oil, which is frequently consumed as a dietary supplement, was shown to have only limited effects.

Karin Zimmer concludes that cortisol synthesis appears to be a sensitive target for POPs and that efforts should be made to find out to what degree this may threaten human and animal health.

Karin Zimmer Cand.med.vet. defended her thesis entitled "Persistent organic pollutants as endocrine disruptors: effects on adrenal development and steroidogenesis" at The Norwegian School of Veterinary Science on 2nd December 2010.